.TH PREDICT 1 "15 May 2006" "KD2BD Software" "KD2BD Software"
.SH NAME
predict \- Track and predict passes of satellites in Earth orbit

.SH SYNOPSIS
predict [-u \fItle_update_source\fP] [-t \fItlefile\fP]
[-q \fIqthfile\fP] [-a \fIserial_port\fP] [-a1 \fIserial_port\fP]
[-n \fInetwork_port\fP]
[-f \fIsat_name starting_date/time ending_date/time\fP]
[-p \fIsat_name starting_date/time\fP]
[-o \fIoutput_file\fP] [-s] [-east] [-west] [-north] [-south]

.SH DESCRIPTION
\fBPREDICT\fP is a multi-user satellite tracking and orbital prediction
program written under the Linux operating system by John A. Magliacane,
KD2BD. \fBPREDICT\fP is free software. You can redistribute it and/or
modify it under the terms of the GNU General Public License as published
by the Free Software Foundation, either version 2 of the License or any
later version.

\fBPREDICT\fP is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY, without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.

.SH FIRST TIME USE
\fBPREDICT\fP tracks and predicts passes of satellites based on the
geographical location of the ground station, the current date and time
as provided by the computer system's clock, and Keplerian orbital data
for the satellites of interest to the ground station. First time users
of \fBPREDICT\fP are provided default ground station location and orbital
data information files. These files are managed by the program, and are
normally located in a user's home directory under a hidden subdirectory
named \fI.predict\fP. First time users will be prompted to supply
\fBPREDICT\fP with their geographical location (the same as selecting
option \fB[G]\fP from the program's main menu) the first time the
program is run. Latitude is normally expressed in degrees north with
latitudes south of the equator expressed in negative degrees. Longitude
is normally expressed in degrees west with eastern longitudes expressed
in negative degrees. This behavior can be modified by passing the
\fI-east\fP or \fI-south\fP commmand line switches to \fBPREDICT\fP.

Latitudes and longitudes may be either entered in decimal degrees, or
in degrees, minutes, seconds (DMS) format.  Station altitude is entered
as the number of meters the ground station is located above sea level.
This parameter is not very critical.  If unsure, make a realistic guess
or simply enter 0.

Users of \fBPREDICT\fP need Keplerian orbital data for the satellites
they wish to track that is preferably no older than one month. The default
orbital data supplied with the program is liable to be quite old, and so
must be brought up to date if accurate results are to be expected. This
may be accomplished by selecting option \fB[E]\fP from \fBPREDICT's\fP
main menu and manually entering Keplerian data for each satellite in
the program's database, or by selecting option \fB[U]\fP and specifying
a file containing recent 2-line Keplerian element data sets that
correspond to the satellites in the program's database.  Keplerian
orbital data is available from a variety of sources, including
\fIhttp://www.celestrak.com/\fP, \fIhttp://www.space-track.org/\fP,
and \fIhttp://www.amsat.org/\fP.

.SH PROGRAM OPERATION
The start-up screen of \fBPREDICT\fP lists the program's main functions.
Several tracking and orbital prediction modes are available, as well as
several utilities to manage the program's orbital database.

.SH PREDICTING SATELLITE PASSES
Orbital predictions are useful for determining in advance when a satellite
is expected to come within range of a ground station. They can also be
used to look back to previous passes to help to confirm or identify past
observations.

\fBPREDICT\fP includes two orbital prediction modes to predict any pass
above a ground station (main menu option \fB[P]\fP), or list only those
passes that might be visible to a ground station through optical means
(main menu option \fB[V]\fP). In either mode, the user is asked to
select a satellite of interest from a menu, and then asked to enter
the date and time (in UTC) at which prediction calculations should
start.

The current date and time may be selected by default by entering nothing
and hitting simply the ENTER key when prompted to enter the starting
date and time.

Otherwise, the starting date and time should be entered in the form:

	\fIDDMonYY HH:MM:SS\fP

Entering the time is optional.  If it is omitted, midnight (00:00:00)
is assumed.  Once complete, orbital calculations are started and
prediction information is displayed on the screen.

The date and time in UTC, along with the satellite's elevation above
ground, azimuth heading, modulo 256 orbital phase, sub-satellite point
latitude and longitude, slant range between the ground station and
the satellite, and the satellite's orbit number are all displayed.
If spacecraft attitude parameters (ALAT, ALON) are included in
\fBPREDICT's\fP transponder database file, then spacecraft antenna
squint angles are displayed instead of orbit numbers in the orbital
prediction output.

An asterisk (*) displayed to the right of the orbit number or squint
angle means the satellite is in sunlight at the date and time listed
on the line. A plus symbol (+) means the satellite is in sunlight
while the ground station is under the cover of darkness at the time
and date listed.  Under good viewing conditions, large satellites
such as the International Space Station (ISS), the US Space Shuttles,
and Hubble Space Telescope, and the Upper Atmosphere Research Satellite
(UARS) are visible to the naked eye. If no symbol appears to the right
of each line, then the satellite is in the Earth's shadow at the time
and date listed, and is not receiving any illumination from the sun.

Pressing the \fBENTER\fP key, the '\fBY\fP' key, or the space bar
advances the orbital predictions to a screen listing the next available
passes.  Pressing the '\fBL\fP' key allows the currently displayed
screen plus any subsequent screens to be logged to a text file in
your current working directory. The name given to this file is the
name of the satellite plus a ".txt" extension.  Any slashes or spaces
appearing in the satellite name are replaced by the underscore (_)
symbol. The logging feature may be toggled on and off at any time by
pressing the '\fBL\fP' key. Exiting the orbital prediction mode by
pressing '\fBN\fP' or hitting the \fBESC\fPape key will also close the
log file. The log file will be appended with additional information
if additional predictions are conducted for the same satellite with
the logging feature turned on.

Selecting \fB[V]\fP from \fBPREDICT's\fP main menu will permit
a ground station to only predict passes for satellites that are
potentially visible through optical means. Since all other passes are
filtered out in this mode, and since some satellites may never arrive
over a ground station when optical viewing conditions are possible,
the program provides the option of breaking out of visual orbital
prediction mode by pressing the \fB[ESC]\fPape key as calculations
are made. A prompt is displayed at the bottom of the screen to alert
the user of this option.

In either orbital prediction mode, predictions will not be attempted
for satellites that can never rise above the ground station's horizon,
or for satellites in geostationary orbits. If a satellite is in range
at the starting date and time specified, \fBPREDICT\fP will adjust the
starting date back in time until the point of AOS so that the prediction
screen displays the first pass in its entirety from start to finish.

.SH SINGLE SATELLITE TRACKING MODE
In addition to predicting satellite passes, \fBPREDICT\fP allows
satellites to be tracked in real-time using \fBPREDICT's\fP
Single Satellite Tracking Mode (main menu option \fB[T]\fP), or
simultaneously as a group of 24 using the program's Multi-Satellite
Tracking Mode (main menu option \fB[M]\fP).  The positions of the
Sun and Moon are also displayed when tracking satellites in real-time.

Selecting option \fB[T]\fP from \fBPREDICT's\fP main menu places the
program in Single Satellite Tracking Mode. The user will be prompted
to select the satellite of interest, after which a screen will appear
and display tracking positions for the satellite selected.

In Single Satellite Tracking Mode, a wealth of information related
to tracking a spacecraft and communicating through its transponder
is displayed.  The current date and time is displayed along with
the satellite's sub-satellite point, its orbital altitude in both
kilometers and statute miles, the slant range distance between the
ground station and the satellite in both kilometers and statute
miles, the current azimuth and elevation headings toward the
satellite, the orbital velocity of the satellite in both kilometers
per hour and statute miles per hour, the footprint of the satellite
in both kilometers and statute miles, the modulo 256 orbital phase
of the satellite, the eclipse depth, the spacecraft antenna squint
angle, and orbital model in use, as well as the current orbit number
are also displayed.  The date and time for the next AOS is also
provided.

Additionally, if the satellite is currently in range of the ground
station, the amount of Doppler shift experienced on uplink and
downlink frequencies, path loss, propagation delay, and echo times
are also displayed.  The expected time of LOS is also provided. 

Uplink and downlink frequencies are held in \fBPREDICT's\fP transponder
database file \fIpredict.db\fP located under \fI$HOME/.predict\fP.
A default file is provided with \fBPREDICT\fP.

Transponders may be selected by pressing the SPACE BAR.  The passband
of the transponder may be tuned in 1 kHz increments by pressing the
\fB<\fP and \fB>\fP keys.  100 Hz tuning is possible using the
\fB,\fP and \fB.\fP keys.  (These are simply the \fB<\fP and
\fB>\fP keys without the SHIFT key.)

If no transponder information is available, the data displayed on
the tracking screen is abbreviated.

The features available in the Single Satellite Tracking Mode make
it possible to accurately determine the proper uplink frequency to
yield a given downlink frequency, or vice versa.  For example, if
one wishes to communicate with a station heard on 435.85200 MHz
via FO-29, then 435.85200 MHz can be selected via the keyboard
as an RX frequency using the tuning keys while tracking FO-29,
and the corresponding ground station TX frequency will be displayed
by \fBPREDICT\fP.

Obviously, an accurate system clock and up-to-date orbital data
are required for the best tuning accuracy.

If a sound card is present on your machine and the Single Satellite
Tracking Mode is invoked with an uppercase '\fBT\fP' rather than
a lowercase '\fBt\fP', \fBPREDICT\fP will make periodic voice
announcements stating the satellite's tracking coordinates
in real-time. Announcements such as:

\fI"This is PREDICT.  Satellite is at fifty six degrees azimuth and forty
five degrees elevation, and is approaching.  Satellite is currently
visible."\fP

are made at intervals that are a function of how quickly the satellite is
moving across the sky. Announcements can occur as frequently as every 50
seconds for satellites in low earth orbits such as the International Space
Station (370 km), or as infrequently as every 8 minutes for satellites in
very high orbits, such as the AMC-6 geostationary satellite (35780 km). Voice
announcements are performed as background processes so as not to interfere
with tracking calculations as the announcements are made. Alarms and special
announcements are made when the satellite being tracked enters into or out
of eclipse. Regular announcements can be forced by pressing the '\fBT\fP'
key in Single Satellite Tracking Mode.

.SH MULTI-SATELLITE TRACKING MODE
Selecting \fB[M]\fP from \fBPREDICT's\fP main menu places the program in a
real-time multi-satellite tracking mode. In this mode, all 24 satellites in
the program's database are tracked simultaneously along with the positions
of the Sun and Moon. Tracking data for the satellites is displayed in
two columns of 12 satellites each. The name, azimuth heading, elevation,
sub-satellite point latitude (in degrees North) and longitude (in degrees
West) positions are provided, along with the slant range distance between
the satellite and the ground station (in kilometers).

A letter displayed to the right of the slant range indicates the satellite's
sunlight and eclipse conditions. If the satellite is experiencing an eclipse
period, an \fBN\fP is displayed. If the satellite is in sunlight and the
ground station is under the cover of darkness, a \fBV\fP is displayed to
indicate the possibility that the satellite is visible under the current
conditions. If the satellite is in sunlight while conditions at the ground
station do not allow the satellite to be seen, a \fBD\fP is displayed.
Satellites in range of the ground station are displayed in \fBBOLD\fP
lettering. The AOS dates and times for the next three satellites predicted
to come into range are displayed on the bottom of the screen between the
tracking coordinates of the Sun and Moon.  Predictions are not made for
satellites in geostationary orbits or for satellites so low in inclination
and/or altitude that they can never rise above the horizon of the ground
station.

.SH SOLAR ILLUMINATION PREDICTIONS
Selecting \fB[S]\fP from \fBPREDICT's\fP main menu will allow solar
illumination predictions to be made.  These predictions indicate how
much sunlight a particular satellite will receive in a 24 hour period.
This information is especially valuable to spacecraft designers and
satellite ground station controllers who must monitor spacecraft power
budgets or thermal conditions on-board their spacecraft due to sunlight
and eclipse periods.  It can even be used to predict the optimum times
for astronauts to perform extra-vehicular activities in space. Solar
illumination predictions may be logged to a file in the same manner
that orbital predictions may be logged (by pressing \fBL\fP).

.SH SOLAR AND LUNAR ORBITAL PREDICTIONS
In addition to making orbital predictions of spacecraft, \fBPREDICT\fP
can also predict transits of  the Sun and the Moon.  Lunar predictions
are initiated by selecting \fB[L]\fP from \fBPREDICT\fP's Main Menu.
Solar predictions are selected through Main Menu option \fB[O]\fP.

When making solar and lunar orbital predictions, \fBPREDICT\fP provides
azimuth and elevation headings, the right ascension, declination,
Greenwich Hour Angle (GHA), radial velocity, and normalized distance
(range) to the Sun or Moon.  Declination and Greenwich Hour Angle
correspond to the latitude and longitude of the object's sub-satellite
point above the Earth's surface.  The radial velocity corresponds to
the speed and direction the object is traveling toward (+) or away
(-) from the ground station, and is expressed in meters per second.
When the radial distance of the Moon is close to zero, the amount of
Doppler shift experienced in Moonbounce communications is minimal.
The normalized distance corresponds to the object's actual distance
to the ground station divided its average distance.  In practice,
the normalized distance can range from about 0.945 to 1.055 for
the Moon, and about 0.983 to 1.017 for the Sun.

Note that the effects of atmospherics are ignored in determining
the elevation angles for the Sun and Moon. Furthermore, the data
provided by \fBPREDICT\fP corresponds to the object's center, and
not the upper or lower limb, as is sometimes done when predicting
the rising and setting times of these celestial objects.

.SH OPERATION UNDER THE X-WINDOW SYSTEM
\fBPREDICT\fP may be run under the X-Window System by invoking it through
the \fIxpredict\fP script contained with this software. \fIxpredict\fP
can invoke \fIrxvt\fP, \fIxterm\fP, \fIEterm\fP, \fIgnome-terminal\fP,
or \fIkvt\fP, and display \fBPREDICT\fP in a virtual terminal window.
\fIxpredict\fP should be edited for best results.  In many cases,
holding down the SHIFT key while pressing the plus (+) and minus (-)
keys allows \fBPREDICT's\fP window to be re-sized when started under
\fIxpredict\fP.

.SH COMMAND LINE ARGUMENTS
By default, \fBPREDICT\fP reads ground station location and orbital
data information from a pair of files located in the user's home directory
under a hidden subdirectory named \fI.predict\fP. Ground station location
information is held in a file named \fIpredict.qth\fP, while orbital data
information for 24 satellites is held in a file named \fIpredict.tle\fP.

If we wish to run \fBPREDICT\fP using data from alternate sources
instead of these default files, the names of such files may be passed
to \fBPREDICT\fP on the command line when the program is started. For
example, if we wish to read the TLE file \fIvisual.tle\fP and the QTH
file \fIbeach_house.qth\fP rather than the default files, we could start
\fBPREDICT\fP and pass the names of these alternate files to the
program in the following manner:

	\fIpredict -t visual.tle -q beach_house.qth\fP

or

	\fIpredict -q beach_house.qth -t visual.tle\fP

If the files specified are not located in the current working directory,
then their relative or absolute paths should also be specified along
with their names (\fIpredict -t /home/kd2bd/orbs/visual.tle\fP).

It is also possible to specify only one alternate file while using the
default for the other. For example,

	\fIpredict -t visual.tle\fP

reads QTH information from the default \fI~/.predict/predict.qth\fP
location, and TLE information from \fIvisual.tle\fP, while

	\fIpredict -q bobs.qth\fP

reads QTH information from \fIbobs.qth\fP and TLE information from the
default \fI~/.predict/predict.tle\fP location.

.SH "QUIET" ORBITAL DATABASE UPDATES
It is also possible to update \fBPREDICT's\fP satellite orbital database
using another command line option that updates the database from a NASA
two-line element data set. \fBPREDICT\fP then quietly exits without
displaying anything to the screen, thereby eliminating the need for
entering the program and selecting the appropriate menu options. This
option is invoked using the \fI-u\fP command line switch as follows:

	\fIpredict -u orbs248.tle\fP

This example updates \fBPREDICT's\fP default orbital database with the
Keplerian elements found in the file \fIorbs248.tle\fP. \fBPREDICT\fP
may be updated from a list of files as well:

	\fIpredict -u amateur.tle visual.tle weather.tle\fP

If an alternate datafile requires updating, it may also be specified
on the command line using the \fI-t\fP switch as follows:

	\fIpredict -t oscar.tle -u amateur.tle\fP

This example updates the \fIoscar.tle\fP orbital database with the
two-line element data contained in \fIamateur.tle\fP.

These options permit the automatic update of \fBPREDICT's\fP orbital
data files using Keplerian orbital data obtained through automatic
means such as FTP, HTTP, or pacsat satellite download.

For example, the following script can be used to update \fBPREDICT's\fP
orbital database via the Internet:

   \fC#!/bin/sh
   wget -qr www.celestrak.com/NORAD/elements/amateur.txt -O amateur.txt
   wget -qr www.celestrak.com/NORAD/elements/visual.txt -O visual.txt
   wget -qr www.celestrak.com/NORAD/elements/weather.txt -O weather.txt
   /usr/local/bin/predict -u amateur.txt visual.txt weather.txt\fR

To truly automate the process of updating your orbital database, save the
above commands to a file in your home directory (such as \fIkepupdate\fP),
and add the following line to your crontab (type \fIcrontab -e\fP to edit
your crontab):

	\fI0 2 * * * kepupdate\fP

and \fBPREDICT\fP will automatically update its database every day at
2:00 AM.

.SH AUTOMATIC ANTENNA TRACKING
\fBPREDICT\fP is compatible with serial port antenna rotator interfaces
conforming to the EasyComm 2 protocol standard.  This includes the
PIC/TRACK interface developed by Vicenzo Mezzalira, IW3FOL
<http://digilander.iol.it/iw3fol/pictrack.html>, TAPR's EasyTrak Jr.
(currently under development), and Suding Associates Incorporated's
Dish Controllers <http://www.ultimatecharger.com/Dish_Controllers.html>.
The FODTRACK rotator interface is supported through the use of Luc
Langehegermann's (LX1GT) \fBfodtrack\fP utility written for and
included with \fBPREDICT\fP.

Using any of these hardware interfaces, \fBPREDICT\fP can automatically
control the position of AZ/EL antenna rotators, and keep antennas
accurately pointed toward a satellite being tracked by \fBPREDICT\fP.
In operation, tracking data from \fBPREDICT\fP is directed to the
specified serial port using the \fI-a\fP command line option.  For
example:

	\fIpredict -a /dev/ttyS0\fP

will send AZ/EL tracking data to the first serial port when the program
is tracking a satellite in the Single Satellite Tracking Mode.  The data
sent to the serial port is of the form: \fIAZ241.0 EL26.0\fP using
9600 baud, 8-data bits, 1-stop bit, no parity, and no handshaking.  Data
is sent to the interface if the azimuth or elevation headings change by
one degree or more.  For interfaces requiring keepalive updates at
least once per second whether the AZ/EL headings have changed or
not (such as the ones by SAI), the \fI-a1\fP option
may be used:

	\fIpredict -a1 /dev/ttyS0\fP

.SH ADDITIONAL OPTIONS
The \fI-f\fP command-line option, when followed by a satellite name or
object number and starting date/time, allows \fBPREDICT\fP to respond
with satellite positional information.  This feature allows \fBPREDICT\fP
to be invoked within other applications that need to determine the
location of a satellite at a particular point in time, such as the
location of where a CCD camera image was taken by a Pacsat satellite
based on its timestamp.

The information produced includes the date/time in Unix format (the
number of seconds since midnight UTC on January 1, 1970), the date/time
in ASCII (UTC), the elevation of the satellite in degrees, the azimuth
heading of the satellite, the orbital phase (modulo 256), the latitude
and longitude of the satellite's sub-satellite point at the time
specified, the slant range to the satellite in kilometers with
respect to the ground station's location, the orbit number, and
the spacecraft's sunlight visibility information.

The date/time must be specified in Unix format (number of seconds since
midnight UTC on January 1, 1970).  If no starting or ending time is
specified, the current date/time is assumed and a single line of output
is produced.  If a starting and ending time are specified, a list of
coordinates beginning at the starting time/date and ending with the
ending time/date will be returned by the program with a one second
resolution.  If the letter \fIm\fP is appended to the ending time/date,
then the data returned by the program will have a one minute resolution.
The \fI-o\fP option allows the program to write the calculated data to
an output file rather than directing it to the standard output device
if desired.

The proper syntax for this option is as follows:

	\fIpredict -f ISS 977446390 977446400 -o datafile\fP

A list of coordinates starting at the current date/time and
ending 10 seconds later may be produced by the following command:

	\fIpredict -f ISS +10\fP

If a list of coordinates specifying the position of the satellite
every minute for the next 10 minutes is desired, the following
command may be used:

	\fIpredict -f ISS +10m\fP

If a satellite name contains spaces, then the entire name must be
enclosed by "quotes".

The \fI-p\fP option allows orbital predictions for a single pass to
be generated by \fBPREDICT\fP via the command-line.  For example:

	\fIpredict -p OSCAR-11 1003536767\fP

starts predictions for the OSCAR-11 satellite at a Unix time of
1003536767 (Sat 20Oct01 00:12:47 UTC).  If the starting date/time
is omitted, the current date/time is used.  If a pass is already
in progress at the starting date/time specified, orbital predictions
are moved back to the beginning of AOS of the current pass, and data
for the entire pass from AOS to LOS is provided.

When either the \fI-f\fP or \fI-p\fP options are used, \fBPREDICT\fP
produces an output consisting of the date/time in Unix format, the
date and time in ASCII (UTC), the elevation of the satellite in
degrees, the azimuth of the satellite in degrees, the orbital phase
(modulo 256), the latitude (N) and longitude (W) of the satellite's
sub-satellite point, the slant range to the satellite (in kilometers),
the orbit number, and the spacecraft's sunlight visibility information.
For example:
\fC
1003611710 Sat 20Oct01 21:01:50   11    6  164   51   72   1389  16669 *
\fR
The output isn't annotated, but then again, it's meant to be read by
other software.

.SH SERVER MODE
\fBPREDICT's\fP network socket interface allows the program to
operate as a server capable of providing tracking data and other
information to client applications using the UDP protocol.  It
is even possible to have the \fBPREDICT\fP server and client
applications running on separate machines provided the clients
are connected to the server through a functioning network connection.

The \fI-s\fP switch is used to start \fBPREDICT\fP in server mode:

	\fIpredict -s\fP

By default, \fBPREDICT\fP uses socket port 1210 for communicating with
client applications.  Therefore, the following line needs to be added
to the end your \fI/etc/services\fP file:

	\fIpredict   1210/udp\fP

The port number (1210) can be changed to something else if desired.
There is no need to recompile the program if it is changed.  To
run more than one instance of \fBPREDICT\fP in server mode on a
single host, an alternate port must be specified when invoking
the additional instances of \fBPREDICT\fP.  This can be
accomplished by using the \fI-n\fP switch:

	\fIpredict -n 1211 -t other_tle_file -s\fP

When invoked in server mode, \fBPREDICT\fP immediately enters
Multi-Satellite Tracking Mode, and makes live tracking data available
to clients.  Clients may poll \fBPREDICT\fP for tracking data
when the program is running in either the Multi-Satellite or Single
Satellite Tracking Mode.  When in Multi-Satellite Tracking mode,
tracking data for any of the 24 satellites in the program's database
may be accessed by client applications.  When in Single-Satellite
Tracking mode, only live tracking data for the single satellite
being tracked may be accessed.  Either tracking mode may be ended
at any time.  When this is done, \fBPREDICT\fP will return the
last calculated satellite tracking data until the program is
again put into a real-time tracking mode.  This allows the user
to return to the main menu, and use other features of the program
without sending potentially harmful data to client applications.

The best way to write a client application is to use the demonstration
program (demo.c) included in this distribution of \fBPREDICT\fP as
a guide.  The sample program has comments to explain how each component
operates.  It is useful to pipe the output of this program through
\fIless\fP to easily browse through the data returned (\fIdemo | less\fP).

In operation, a character array is filled with the command and arguments
to be sent to \fBPREDICT\fP.  A socket connection is then opened, the
request is sent, a response is received, and the socket connection
is closed.  The command and arguments are in ASCII text format.

Several excellent network client applications are included in this
release of \fBPREDICT\fP, and may be found under the \fIpredict/clients\fP
directory.

.SH ADDING SATELLITES
One of the most frequently asked questions is how satellites in
\fBPREDICT's\fP orbital database may be added, modified, or replaced.
As it turns out, there are several ways in which this can be done.
Probably the easiest is to manually edit your
\fI~/.predict/predict.tle\fP file, and replace an existing
satellite's entry with 2-line Keplerian data for the new satellite.
If this method is chosen, however, just make sure to include ONLY
the two line data, and nothing else.

Another way is to is select the Keyboard Edit option from the program's
Main Menu, select a satellite you wish to replace.  Edit the name and
object number (replacing the old information with the new information).
Just hit ENTER, and accept all the other orbital parameters shown.  Get
back to \fBPREDICT's\fP Main Menu.  Select Auto Update, and then enter
the filename containing the 2-line element data for your favorite new
satellite.  The new satellite data should be detected by \fBPREDICT\fP,
and the orbital data for the old satellite will be overwritten by the
new data.

.SH NEAT TRICKS
In addition to tracking and predicting passes of satellites, \fBPREDICT\fP
may also be used to generate a NASA two-line Keplerian element data set
from data entered via keyboard. For example, let's say you're listening
to Space Shuttle audio re-broadcasts via WA3NAN and Keplerian elements
for the Space Shuttle's orbit are given by the announcer. The orbital
data provided by WA3NAN in verbal form may be manually entered into
\fBPREDICT's\fP orbital database using option \fB[E]\fP of the program's
main menu (Keyboard Edit of Orbital Database). The orbital data for the
Space Shuttle in NASA two-line element form can then be found in your
orbital database file, and may imported to any other satellite tracking
program that accepts two-line element files or distributed to others
electronically.

It is also possible to run \fBPREDICT\fP as a background process and
direct its display to an unused virtual console by using the following
command:

        \fIpredict < /dev/tty8 > /dev/tty8 &\fP

Switching to virtual console number 8 (ALT-F8 in text mode) will
allow \fBPREDICT\fP to be controlled and displayed even after you've
logged out.  This is especially handy when running \fBPREDICT\fP in
server mode on a remote machine.

.SH GLOSSARY OF TERMS
The following terms are frequently used in association with satellite
communications and space technology:

.SH AOS:
Acquisition of Signal - the time at which a ground station first acquires
radio signals from a satellite. \fBPREDICT\fP defines AOS as the time
when the satellite being tracked comes within +/- 0.03 degrees of the
local horizon, although it may have to rise higher than this before
signals are first heard.
.SH Apogee:
Point in a satellite's orbit when the satellite is at its farthest
distance from the earth's surface.
.SH Anomalistic Period:
A satellite orbital parameter specifying the time between successive
perigees.
.SH Ascending Node:
Point in a satellite's orbit when its sub-satellite point crosses the
equator moving south to north.
.SH Azimuth:
The compass direction measured clockwise from true north.  North = 0
degrees, East = 90 degrees, South = 180 degrees, and West = 270 degrees.
.SH Descending Node:
Point in a satellite's orbit when its sub-satellite point crosses the
equator moving north to south.
.SH Doppler Shift:
The motion of a satellite in its orbit around the earth, and in many cases
the rotational motion of the earth itself, causes radio signals generated
by satellites to be received on Earth at frequencies slightly different
than those upon which they were transmitted. \fBPREDICT\fP calculates
what effect these motions have upon the reception of satellites
transmitting on the 146 MHz and 435 MHz Amateur Radio bands.
.SH Elevation:
The angle between the local horizon and the position of the satellite. A
satellite that appears directly above a particular location is said to be
located at an elevation of 90 degrees. A satellite located on the horizon
of a particular location is said to be located at an elevation of 0 degrees.
A satellite with an elevation of less than zero is positioned below the
local horizon, and radio communication with a satellite in such a position
is not possible under normal circumstances.
.SH Footprint:
Diameter of the Earth's surface visible from a satellite.  The higher
the satellite's orbital altitude, the greater the footprint, and the
wider the satellite's communications coverage.
.SH LOS:
Loss of Signal - the time at which a ground station loses radio contact
with a satellite. \fBPREDICT\fP defines LOS as the time when the satellite
being tracked comes within +/- 0.03 degrees of the local horizon.
.SH Orbital Phase:
An orbital "clock" that describes a satellite's orbital position with
respect to perigee. Orbital Phase may be modulo 256, or modulo 360, and
is sometimes referred to as mean anomaly when speaking of amateur radio
satellites in elliptical orbits, such as the Phase 3 satellites.
Orbital phase is zero at perigee.
.SH Path Loss:
The apparent attenuation a radio signal undergoes as it travels a given
distance. This attenuation is the result of the dispersion radio waves
experience as they propagate between transmitter and receiver using
antennas of finite gain. Free space path loss is technically an
oxymoron since free space is loss free.
.SH Perigee:
Point in a satellite's orbit when the satellite is at its closest
distance to the earth's surface.
.SH Nodal Period:
A satellite orbital parameter specifying the time between successive
ascending nodes.
.SH Slant Range:
The straight line distance between the ground station and the satellite
at a given time.
.SH Sub-Satellite Point:
The latitude and longitude specifying the location on the Earth that
is directly below the satellite.

.SH ADDITIONAL INFORMATION
Detailed information on the operation of \fBPREDICT's\fP UDP socket-based
interface as well as sample code for writing your own client applications
is available in the \fIpredict/clients/samples\fP subdirectory.  The latest
news is available through the official \fBPREDICT\fP software web page
located at: <http://www.qsl.net/kd2bd/predict.html>.
.SH FILES
.TP
\fC~/.predict/predict.tle\fR
Default database of orbital data
.TP
\fC~/.predict/predict.db\fR
Satellite transponder database file
.TP
\fC~/.predict/predict.qth\fR
Default ground station location information

.SH AUTHORS
\fBPREDICT\fP was written by John A. Magliacane, KD2BD <kd2bd@amsat.org>.
The socket server code was contributed by Ivan Galysh, KD4HBO
<galysh@juno.nrl.navy.mil>.  The PIC/TRACK serial port antenna
rotator controller code was contributed by Vittorio Benvenuti, I3VFJ
<benscosm@iol.it>.  SGP4/SDP4 code was derived from Pacsal routines
written by Dr. T.S. Kelso, and converted to 'C' by Neoklis Kyriazis,
5B4AZ.  See the CREDITS file for additional information.

